1. Field of the Invention
The invention relates to an apparatus for transcutaneous electric nerve stimulation (TNS) with a power supply, a frequency generator and an electric circuit for variable frequency and intensity electrode output signals connectable with the apparatus and an output short circuit to improve the pulse form emitted.
2. Description of the Related Technology
Various kinds of painful conditions have been treated by electric nerve stimulation by stationary devices. These methods are standard physical therapy. These processes involve application of current to the skin. A high stress is applied to the skin by a direct current and currents of a DC character. However, the depth of current penetration, which is important to the treatment of numerous painful conditions, is very low.
Only by the development of electronic structural elements, in particular semiconductors, has it been possible to produce pulsed currents and frequencies of different kinds and to determine their therapeutic effects.
By virtue of technical developments in the field of power sources and electronic miniaturization, small portable therapy devices suitable for adequate continuous use were developed. The decisive difference between the high voltage devices designed for stationary use and the portable TNS is merely different power outputs. An effective and adequate current density may be obtained with TNS devices by the use of relatively small electrode surfaces, which are entirely sufficient, as the concentration and strength of this form of treatment applies to local pain therapy.
It was found in actual practice that the pulse form emitted by TNS devices is not entirely suitable for the actual characteristics of TNS applications. Current intensity measurements were performed heretofore on a purely ohmic load resistor, with their value amounting in most cases in about 1 KOhm. The resultant pulse form corresponds to a square pulse with steep flanks.
It has been discovered in practice that the equivalent network diagram does not consist of purely ohmic resistors, but of a series of horizontal load resistors with a parallel connected capacitor on one resistor. The pulse forms obtained in this manner greatly differ from those mentioned above.
It has been found that the dimensioning of the structural elements in the simplified equivalent network diagram depends on a number of parameters, i.e., the type of skin of the patient, the electrode gel used, the electrodes and the frequency applied.
It was also discovered that the current measured on the patient is higher than at the 1 KOhm measuring resistor. Finally, the voltage pulse determined on the patient is strongly rounded, i.e., the rise flattens after a steep onset to a maximum, which decreases steeply and declines asymptotically. The correct pulse is saw-tooth like, with a strongly negative pulse.